It is the closest star we’ll ever see. It is about
5 billion years old, and will live for about 5
billion more years. But not all stars live this long.
Really big stars, those 10–20 times bigger than
the Sun, live only a few million years. And when
they burn out, they go out with a bang!

RUNNING OUT OF GAS

The energy from a star is the result of gravity,
which pulls all of its matter toward its center. This
compresses the center and makes it so hot that
fuel there undergoes a process called nuclear fusion.
This fusion releases energy that holds up
the outside of the star against gravity. But when
the center runs out of fuel, the outer layers come
crashing down. Stars like the Sun get crushed
to the size of the Earth in this process. For stars
much larger than the Sun, this process causes
a massive explosion. These supernova explosions
blow the star apart and, for several days,
generate more light than a billion stars.

SUPERNOVA 1987A

In February of 1987, a university student was
working at a telescope in Chile. He looked at the
pictures he had just taken with the telescope and
saw a very bright object that he knew he hadn’t
seen before—and he knew this part of the sky
very well. He went outside, looked up, and could
see it with his naked eye. He had discovered
a supernova! In this case, we actually have pictures
of the star before it blew up. It was a giant
blue star, and pictures of that region show the star
is no longer there. But pictures with the Hubble
Space Telescope show rings of matter that were
thrown out from the star before the explosion. The
outer rings were thrown out about 20,000 years
ago. The Chandra X-ray Observatory shows us
that the explosion is now reaching the inner ring,
making it so hot that it glows in X-rays!

THE CRAB NEBULA

In 1054, Chinese astronomers recorded the sudden
brightening of a star. It was so bright that
it could be seen during the day for months!
They had witnessed a supernova. The explosion
in 1054 left behind the Crab Nebula, a bright fuzzy
looking object with very energetic particles. The Crab
Nebula can still be seen with a small telescope.